1. Field of the Invention
The present invention relates to simple and complex metal soap thickened poly alpha olefin base greases containing additional lubricating oil constitutents said greases exhibiting enhanced thermal stability and improved thickener utilization resulting in improved grease yields.
2. Description of the Related Art
The grease lubrication of paper machine bearings is a considerable challenge due to the wide range of conditions that exist throughout the machine. In the wet end of the paper machine (i.e., forming and press sections), ambient temperatures are generally moderate (30 to 40.degree. C.), with the grease being subjected to severe water washing. In the dryer-section, ambient temperatures may range from 90.degree. C. to as high as about 140.degree. C., with exposure to water vapor being a significant problem. Wet end wire-roll and press-roll bearings may be very large (usually double spherical roller type with 400 to 500 mm bore diameter). In the dryer sections, bearings are generally smaller (80 to 150 mm bore diameter), but operate at higher speeds.
Historically, paper machine OEM's have recommended different greases for these different parts of the machine. In the wet end, the greases recommended are generally of a softer consistency (NLGI #1), and require extreme pressure additives to provide bearing protection where boundary conditions may develop at relatively low operating temperatures. In the dryer-section, NLGI #2 greases with higher base fluid viscosities are suggested, and the use highly active extreme pressure agents is discouraged. Greases are offered in the marketplace for use throughout paper machines operating under severe conditions; these generally incorporate a 100% synthetic hydrocarbon base oil, which can create problems with respect to controlling the amount of soap present in the grease.
The production of simple soap and complex soap/salt thickened greases and techniques for improving grease yields have, however, long been practiced.
U.S. Pat. No. 3,159,575 teaches a process for improving grease yields of calcium soap/salt thickened greases by adding alkyl methacrylate-vinyl pyrolidone copolymers to the grease. The base oil vehicle for such greases is described as mineral oil exemplified by naphthenic oil, paraffinic oil and mixed base oils derived from petroleum, including lubricating oils derived from coal products, etc.
U.S. Pat. No. 3,159,576 also teaches a method for improving grease yield of calcium soap/salt thickened greases by adding quaternary ammonium compounds to the grease in combination with the calcium soap/salt thickener.
U.S. Pat. No. 3,189,543 similarly teaches a method for improving grease yield of calcium soap/salt thickened greases by incorporating an oil soluble poly glycol substituted polymer into the grease.
In the preceding patents the greases were made by producing the calcium soap/salt thickener in a first portion of the final grease mineral base oil, adding the specified yield improving polymeric or quaternary ammonium compound additive then adding the balance of the mineral base oil to make the total of 100% of the specified mineral oil.
U.S. Pat. No. 3,681,242 teaches a two stage process for the production of high dropping point lithium soap/salt thickened grease. In the process the complex lithium soap/salt thickener is prepared in a first portion of base oil. This first portion of base oil corresponds to between 30% to 75% of the total amount of oil which will be present in the final grease. The fatty acids and dicarboxylic acids are heated with stirring in this first base oil portion to about 180-210.degree. F. Concentrated aqueous solution of lithium hydroxide is then slowly added and heated to 290-3 10.degree. F. to insure elimination of water. The temperature is then further raised to at least 410.degree. F. but no higher than 430.degree. F. The balance of the base oil used to make the grease is then added to this mixture and the temperature is rapidly reduced to about 220.degree. F. after which the mixture is reheated to about 350-375.degree. F. followed by immediate rapid cooling to a temperature in the range 220-240.degree. F. The mixture is held at this temperature for 8 to 16 hours then passed through a mill and cooled to room temperature.
Again, the oils used as the first and second (or balance) positions of oil employed are the same in each case.
U.S. Pat. No. 3,428,562 teaches a process for preparing a lithium grease composition containing synthetic oil as the sole lubricating oil component. The synthetic oils of interest is ester type synthetic lubricating oils. In this procedure fatty acid is saponified with aqueous lithium hydroxide at a temperature of 160-200.degree. F. after which 23-41 wt % of the synthetic ester type lube oil based on the total weight of oil in the finished grease is added. This is followed by heating at a rate of at least 0.7.degree. F. per minute to a top temperature of between 380 to 450.degree. F. while adding or adding 30 to 56 wt % of the same or different synthetic ester type lube oil. The mixture is held at the aforesaid temperature for from 0 to 30 minutes followed by cooling and the addition of any balance of synthetic ester oil needed to make 100% of the final desired oil content.
U.S. Pat. No. 4,749,502 is directed to a grease composition comprising an oil component having a major amount of a synthetic fluid having a viscosity of at least 50 cSt at 40.degree. C. and a minor amount of a mineral oil having a pour point below -20.degree. C. and a thickener. The synthetic fluid is preferably polyalphaolefin. The thickener comprises the simple lithium, calcium, aluminum and/or barium soaps of fatty acids such as stearic acid or 12-hydroxy stearic acid, or the complex calcium, lithium, barium and/or aluminum soaps/salts of the aforesaid fatty acids with lower molecular weight mono- or dibasic acids.
In U.S. Pat. No. 4,749,502 the viscosity of the mineral oil is lower than the viscosity of the synthetic fluid over the temperature range for which the use is contemplated. In producing the grease a blend of the aforesaid oils was used as the base stock.
U.S. Pat. No. 4,597,881 teaches a process for producing a lithium soap grease comprising the steps of adding a hydroxy fatty acid and dicarboxylic acid to a first base oil having an aniline point of 110.degree. C. to 130.degree. C. at a temperature of less than 100.degree. C. with stirring to prepare a uniform dispersion of acids in the first base oil. Thereafter lithium hydroxide is added to the mixture and the mass is heated to a temperature of 195.degree. C. to 210.degree. C. The mass is cooled to a temperature not higher than about 160.degree. C. at a rate of 20.degree. C. to 80.degree. C. per hour. Finally, a second base oil having an aniline point of from 130.degree. C. to 140.degree. C. is added to the mass so that the weight ratio of the first base oil to the second base oil is from 30:70 to 60:40 and the resulting mixture has a dynamic viscosity of 5 to 50 cSt at 100.degree. C. and an aniline point of from 125.degree. C. to 135.degree. C. The first and second base oils may each have a viscosity in the range 5 to 50 cSt at 100.degree. C. In Examples 3 to 5 the first base oils employed had dynamic viscosities at 100.degree. C. of 11.2 cSt, 11.4 cSt and 11.6 cSt while the corresponding second base oils employed had dynamic viscosities at 100.degree. C. of 19.4 cSt, 19.2 cSt, and 19.2 cSt producing a final grease base oil blend having dynamic viscosities at 100.degree. C. of 14.7 cSt, 14.7 cSt, and 14.8 cSt, respectively. In the case of these base oils, the components blended to make the base oils were 500 neutral oil, bright stock and naphthene mineral oil, no synthetic oils were used.
U.S. Pat. No. 5,364,544 are directed to grease for slide contacts based on synthetic oil which is polyalphaolefin. The PAO base oil consists of a synthetic PAO having a low viscosity of from 8 to 30 cSt at 40.degree. C. and a synthetic PAO having a high viscosity of from more than 30 to about 470 cSt at 40.degree. C. The base oil is apparently employed as a blend of such PAO's of different viscosities.
U.S. Pat. No. 5,133,888 teaches an engine bearing grease comprising a lithium soap thickener, a synthetic base oil blend of polyalphaolefins and extreme pressure anti wear additives and inhibitors comprising dithiocarbamates, phosphates, and hydroxides. In the examples the base oil used was a per se blend of two PAO.
FR 2,572,089 teaches a grease comprising 65 to 94.5 wt % lubricating oil, 25 to 5 wt % lithium soap comprising lithium salts of saturated C.sub.14 -C.sub.24 dihydroxy monocarboxylic acids, and 10-0.5 wt % other additives. The lube oil base is described as preferably being a naphthenic or paraffinic mineral oil or a synthetic oil with a viscosity of 4-30 cSt at 100.degree. C. The synthetic oil may comprise a polyalphaolefin containing a hydrogenated alkyl benzene to solubilize the soaps, or esters such as esters of C.sub.5 -C.sub.10 fatty acids with polyols. An example describes a grease comprising 10 wt % hydrogenated alkyl aromatic, 55 wt % PAO, 15 wt % penta erythritol ester, 15 wt % lithium soap and the balance other additives.